The mechanism of ion transport across the epithelial membrane is the broad objective to this study. Specific foci are to be the detailed relationship betwen metabolism and transport and the nature of the initial sodium-membrane site reaction step at the outer border of the isolated frog skin. In addition to conventional methods of membrane electrochemistry (potentials, currents, steady state isotope fluxes); histology (light, transmission and scanning E.M.); and cellular biophysics (ion content analysis, oxygen consumption) newly developed methods of rapid isotope washout, of relaxation spectral analysis, analysis of power spectra and of isolating large sheets of epidermis will be used. These efforts will be aimed at the construction of a molecular model for sodium transport (a) across the outer surface of frog skin and its alteration by hormonal, pharmacological and other agents and (b) in relation to metabolism of the epidermal cells, particularly cell sodium concentration effects.